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Title: IMPROVING THE BERTHELOT REACTION FOR DETERMINING AMMONIUM IN SOIL EXTRACTS AND WATER

Author
item RHINE, ELIZABETH - UNIV OF ILLINOIS
item SIMS, GERALD
item MULVANEY, RICHARD - UNIV OF ILLINOIS
item PRATT, ELLEN - UNIV OF ILLINOIS

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/15/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Ammonium is an important chemical species that is commonly measured in soil and water for a variety of agricultural and environmental reasons. Present methods for the analysis of ammonium in large numbers of samples can give erroneous measurements if certain metals and organic compounds related to ammonium are present in the sample. In addition, most approaches for ammonium measurement generate large volumes of hazardous waste (up to 1.5 gallons per 100 samples). Studies were performed to discover new chemistry that would allow more specific analysis of ammonium (less interference by other compounds in the sample) and this new chemistry was developed into three methods that would allow laboratories with different equipment to incorporate the new chemistry into the procedures currently in use. One of the three methods was based on microchemical analysis, and has the added benefit of reducing hazardous waste production by up to 100 fold compared to existing methods for ammonium. The results of the studies, and the methods produced will be useful to research, environmental, and soil testing laboratories, especially those attempting to reduce hazardous waste production.

Technical Abstract: Colorimetric methods based on the Berthelot reaction are used widely for quantitative determination of NH4-N in biological and environmental samples. A chelating agent is commonly employed to minimize inorganic interferences in analyses of soil extracts, but organic interferences can also occur. Color development is accomplished using either phenol or salicylate, yet these substrates have not been directly compared. In the present study numerous organic interferences were observed with both compounds. Interferences were observed with both compounds. Interferences differed markedly between phenol and salicylate. The possibility of a simple correction was precluded by the fact that interferences were both positive and negative, and depended upon the temperature during color development and the concentration of NH4-N. fourteen compounds were evaluated as alternatives to phenol and salicylate, of which the Na salt of 2-phenylphenol (PPS) proved to be the most promising. Using PPS, macro- and microscale batch methods and an automated flow-injection method were developed. These methods are simple, convenient, and sensitive. The accuracy and precision of the PPS microscale method was demonstrated through recovery tests with soil extracts. Precipitation of metal hydroxides was controlled by chelation with citrate rather than EDTA, which caused a serious decrease in absorbance. Compared to Berthelot methods that use phenol or salicylate, interference by amino acids was decreased by up to tenfold. Interference by other organic N compounds was virtually eliminated.